CN114480972A

CN114480972A - Thin-specification Ni-free weathering steel produced based on CSP process and production method thereof

Info

Publication number: CN114480972A
Application number: CN202210099740.XA
Authority: CN
Inventors: 何博; 胡学文; 郭锐; 汪飞; 石践; 王海波; 张宇光; 赵海山; 王飞; 舒宏富; 鲍磊; 李耀辉; 史红林; 饶添荣
Original assignee: Maanshan Iron and Steel Co Ltd
Current assignee: Maanshan Iron and Steel Co Ltd
Priority date: 2022-01-27
Filing date: 2022-01-27
Publication date: 2022-05-13

Abstract

The invention provides thin-specification Ni-free weathering steel produced based on CSP process and a production method thereof, and the thin-specification Ni-free weathering steel comprises the following components: c: 0.04% -0.06%, Si: 0.30-0.55%, Mn: 0.30-0.80%, P: 0.020 to 0.150%, S: less than or equal to 0.005 percent, Cr: 0.30-0.80%, Cu: 0.25% -0.40%, Als: 0.015% -0.040%, Ti: 0.010-0.040%, the rest is Fe and inevitable impurity elements. According to the invention, a proper amount of P and Si is added, and through the matching design and interaction of Si-P-Cu-Cr elements, the problems of continuous casting breakout and product surface crack defects caused by copper brittleness are solved, and the manufacturing cost is reduced, and the alloy has good atmospheric corrosion resistance and strong plasticity matching.

Description

Thin-specification Ni-free weathering steel produced based on CSP process and production method thereof

Technical Field

The invention belongs to the field of steel materials, and particularly relates to thin-specification Ni-free weathering steel produced based on a CSP (cast Steel plate) process and a production method thereof.

Background

The weathering steel is also called as atmospheric corrosion resistant steel, has low manufacturing cost compared with the stainless steel with less alloy content, has good atmospheric corrosion resistance compared with common carbon steel, and is widely applied to the industries of railway vehicles, containers, buildings, photovoltaic supports and the like. Cu can obviously improve the atmospheric corrosion resistance of steel, is one of main alloy elements added in weather-resistant steel, but has a melting point of 1083 ℃, and is easy to cause surface quality defects such as steel leakage in the continuous casting production process, edge cracks in the heating and hot rolling processes of a casting blank and the like due to the existence of Cu. In the prior weathering steel, Cu and Ni are often added in a compounding way, Ni/Cu is controlled to be more than or equal to 0.5, a Cu-Ni binary alloy phase with a high melting point is formed, the enrichment of liquid phase copper is inhibited, and the manufacturing problem is solved. However, Ni is a precious alloy element, and the addition of Ni not only increases the manufacturing cost of the weathering steel, but also accelerates the consumption of Ni resources.

The weather-resistant steel plate for the thin gauge plate produced by the CSP thin slab continuous casting and rolling process has the advantages of good plate shape, uniform performance, high rolling stability and the like. But the drawing speed of the continuous casting and rolling process of the thin slab is greatly higher than that of the conventional hot continuous rolling strip process, the reduction rate of the casting blank is low, the risk of bleed-out caused by producing Ni-free weathering steel is aggravated, and meanwhile, the surface of a hot rolled coil has crack defects to influence the use of downstream users.

In the prior art, a publication number CN 105603320 a published in 2016, 5, month and 26 discloses a method for producing a container plate by thin slab continuous casting and rolling, which comprises the following chemical components in percentage by mass: c: 0.05-0.09%, Si: 0.30 to 0.50%, Mn: 0.40-0.60%, P: 0.070-0.120%, S: 0.001-0.015%, Cr: 0.30-0.50%, Ni: 0.03-0.10%, Cu: 0.25 to 0.40%, and the balance of Fe and inevitable impurities. The expensive alloy Ni is added, so the manufacturing cost is higher, and the container is only used for manufacturing containers and has single use.

The publication No. CN 111850396A published in 10, 30 and 2020 of China discloses an economical bainite weathering steel for a container and a CSP line production method, and the bainite weathering steel comprises the following chemical components in percentage by mass: c: 0.051-0.065%, and Si: 0.61-0.85%, Mn: 0.81-1.02%, P: 0.08-0.15%, S: less than or equal to 0.005 percent, Al: 0.015-0.055%, Cu: 0.46-0.61%, Cr: 0.61-0.72%, Ti: 0.026-0.061%, N: less than or equal to 0.006 percent, and the balance of Fe and inevitable impurities. And (3) coiling at the finishing temperature of 758-799 ℃ and the low temperature of 418-511 ℃, wherein the metallographic structure is not less than 95% of bainite by volume. Yield strength: 351-396 MPa, tensile strength: 483-532 MPa, elongation: 36-47%. The invention is suitable for steel plates with the thickness less than or equal to 2.0mm, has high contents of Si, Mn and Cu, and greatly improves the manufacturing cost of the weathering steel. Although Ni is not added, no measures are proposed to solve the copper embrittlement defect at high Cu content. And is only used for manufacturing containers, and has single use.

Disclosure of Invention

The invention aims to provide thin-specification Ni-free weathering steel produced based on CSP process and a production method thereof, which saves precious Ni alloy and reduces the manufacturing cost of the weathering steel; the high-strength steel plate has good atmospheric corrosion resistance and comprehensive mechanical property, and the thickness range of the plate is 1.5-3.0 mm. The method solves the control problem of the surface defects of continuous casting bleed-out and hot rolling of the Ni-free Cu-containing weathering steel produced by the CSP process, realizes the stable batch production of the Ni-free thin high-strength weathering steel plate, and can be used for manufacturing the thin weathering steel used for containers, cable bridges, photovoltaic supports and the like.

The specific technical scheme of the invention is as follows:

the thin-specification Ni-free weathering steel produced based on the CSP process comprises the following components in percentage by mass:

c: 0.04-0.06%, Si: 0.30-0.55%, Mn: 0.30-0.80%, P: 0.020 to 0.150%, S: less than or equal to 0.005 percent, Cr: 0.30-0.80%, Cu: 0.25% -0.40%, Als: 0.015% -0.040%, Ti: 0.010-0.040%, the rest is Fe and inevitable impurity elements.

The thin-specification Ni-free weathering steel produced based on the CSP process also needs to meet the following conditions in terms of chemical component design: the weathering index I of this steel grade was calculated with reference to the formula Legault-Leckie modified in American society for testing and materials Standard ASTM G101-01, I ═ 26.01 (% Cu) +3.88 (% Ni) +1.20 (% Cr) +1.49 (% Si) +17.28 (% P) -7.29 (% Cu) x (% Ni) -9.10 (% Ni) x (% P) -33.39 (% Cu)². The atmospheric corrosion resistance of the material is increased along with the increase of the I value, and when the I value is more than or equal to 6.0, the material has good atmospheric corrosion resistance. The chemical composition design of the invention also needs to meet the requirement that I is more than or equal to 7.0.

The thin-specification Ni-free weathering steel produced based on the CSP process has the structure of polygonal ferrite and pearlite, the average grain size of the ferrite is 8-12 mu m, the volume fraction of the ferrite is 90-92%, and the balance is the pearlite.

The thin-specification Ni-free weathering steel produced based on the CSP process has the following thickness: 1.5-3.0 mm, tensile property: yield strength R_eL380MPa or more, the tensile strength Rm is 490MPa or more, and the elongation A is 28% or more.

The invention provides a production method of thin-specification Ni-free weathering steel based on CSP process production, which comprises the following process flows of: molten iron pretreatment deep desulfurization → converter top and bottom combined blowing → LF refining → thin slab continuous casting → CSP slab heating → CSP hot continuous rolling → laminar cooling → coiling.

Specifically, the sheet bar continuous casting is carried out after molten steel is smelted according to the chemical components.

The thin slab continuous casting specifically comprises the following steps: in the continuous casting process, the thickness of the blank shell is increased by adopting low superheat degree casting, and the lubricating action between the wall of the crystallizer and the blank shell is improved by carrying out protective casting by using special protective slag, so that steel leakage is avoided. Controlling the superheat degree of the molten steel of the tundish at 10-30 ℃; the main physical and chemical performance indexes of the special protective slag are as follows: alkalinity of 0.8-1.3, viscosity of 0.10-0.30 Pa.s, and melting point of 1022-1152 ℃; the thickness of the continuous casting slab is 60-90 mm, and the drawing speed of the continuous casting slab is controlled to be 3.5-4.5 m/min according to the width and the thickness of the casting slab.

The CSP plate blank heating specifically comprises the following steps: after cutting, the casting blank enters a roller hearth type heating furnace to be heated, and the charging temperature is more than or equal to 1000 ℃. And heating the plate blank for 20-35 min at the tapping temperature of 1130-1200 ℃. The low-temperature rapid heating is adopted, the time of a casting blank in a furnace is shortened, and the diffusion and enrichment of liquid phase Cu to an austenite crystal boundary are reduced. The heating furnace adopts a reducing atmosphere, so that the oxidation of Fe on the surface of a casting blank in the heating process is reduced, and the enrichment of liquid-phase copper on the interface of a steel matrix and an iron scale is reduced, thereby improving the surface crack defect generated in the hot rolling process.

The CSP hot continuous rolling specifically comprises the following steps:

removing scale on the surface of the plate blank by high-pressure water after the plate blank is discharged out of the furnace, and then directly rolling by adopting a 7-frame four-roller CVC continuous rolling unit; the reduction rates of F1, F2 and F3 are more than 50%, and the recrystallization of deformed austenite is promoted to refine the grain size at high temperature and high pressure; f6 and F7 are mainly used for improving the plate type of thin steel strips, and the reduction rate is less than 10 percent; the running speed of the strip steel discharging F7 is controlled to be 7-12 m/s. And controlling the finish rolling temperature to be 840-900 ℃, finishing rolling in an austenite non-recrystallization region, and refining the grain size of ferrite after phase transformation. The final rolling temperature is too high, austenite grains grow large, and the material strength is reduced; the final rolling temperature is too low, and the mixed crystal is easy to be formed by rolling in a two-phase region, so that the material shaping is reduced.

The laminar cooling specifically comprises: carrying out laminar cooling at the cooling speed of 50-100 ℃/s after finishing rolling;

the coiling specifically comprises the following steps: the coiling temperature is controlled to be 570-630 ℃. Cooling the laminar flow to 570-630 ℃ for coiling, wherein the coiling temperature is too high, ferrite grains are coarsened, and the strength is insufficient; the bainite structure is generated at the low coiling temperature, the plasticity of the material is reduced, and the forming performance is influenced. And naturally cooling to room temperature after coiling.

The thin-specification Ni-free weathering steel alloy elements produced by the CSP process provided by the invention have the following design principles in percentage by mass:

c (carbon): c is the most economical element for improving the strength of steel, but too high C content deteriorates the weldability of steel and reduces the plasticity. In order to improve the strength of the weathering steel, the content of C is designed to be 0.04-0.06%.

Si (silicon): si is beneficial to refining corrosion products, promotes the formation of a compact protective rust layer on the surface of steel so as to improve the atmospheric corrosion resistance, can also inhibit the enrichment of copper elements on the surface of copper-containing steel after high-temperature oxidation, and improves the surface crack defect generated in the hot rolling process. However, too high Si content may deteriorate the weldability of the steel. Therefore, the Si content is designed to be 0.30-0.55%.

Mn (manganese): mn is one of important solid solution strengthening elements in steel, and improves the strength and toughness of the steel. However, too high Mn content not only increases the production cost of the weathering steel, but also deteriorates the weldability of the steel. Therefore, the content is designed to be 0.30 to 0.80%.

P (phosphorus): p is the most economical element for improving the atmospheric corrosion resistance of the steel and can also play a role in solid solution strengthening, but the excessive P content is easy to segregate in grain boundaries to reduce the low-temperature toughness of the steel and increase the welding crack sensitivity. Therefore, the content of P is designed to be 0.020-0.150%, and low-P or high-P components can be selected according to the requirements of downstream users and the standard requirements of products;

s (sulfur): s is a harmful residual element in steel, and deteriorates the atmospheric corrosion resistance and ductility and toughness of steel. Therefore, the S content is designed to be less than or equal to 0.005 percent

Als (aluminum): al is the main deoxidizing element added into steel, and the bonding force of Al and oxygen is greater than that of Ti. However, too high Al causes the content of Al oxide inclusions in the steel to increase, the atmospheric corrosion resistance of the steel is reduced, and the nozzle is easily blocked by continuous casting. Therefore, the content is designed to be 0.015 to 0.040%.

Cr (chromium): cr is an important alloy element for improving the atmospheric corrosion resistance of steel, and particularly can enrich and promote the generation of a compact protective rust layer on the surface of the steel when being added with Cu in a compounding way, so that the atmospheric corrosion resistance of the steel is obviously improved. Since the welding property of the steel is deteriorated by too high Cr content, the Cr content is designed to be 0.30 to 0.80%.

Cu (copper): cu is a main atmospheric corrosion resistant element and can also precipitate fine second phase particles in the cooling process to improve the strength; however, the melting point of Cu is low, and the content of Cu is too high, which easily causes continuous casting breakout and surface cracks in the hot rolling process, so that the content of Cu is designed to be 0.25-0.40%.

Ti (titanium): ti is a strong nitride forming element, the solid solution temperature of TiN is higher, the growth of austenite grains can be inhibited in the slab heating process, the grain size is refined, the austenite grain interface area is increased, and the enrichment degree of liquid phase copper in the austenite grain boundary is reduced, so that the surface crack defect generated in the hot rolling process is improved; in addition, the strength of the material can be improved. The content is controlled to be 0.010 percent to 0.040 percent.

The invention solves the problems of continuous casting bleed-out and product surface crack defects easily generated by Ni-free weathering steel produced by CSP process through the synergistic design and control of chemical components, continuous casting and heating process, obtains the required microstructure and mechanical property through alloy components and hot continuous rolling process design, and improves the weathering resistance of products.

Compared with the prior art, the method realizes the production of the Ni-free weathering steel in the CSP process, saves the noble metal Ni resource and reduces the manufacturing cost. Meanwhile, through the matching design and the synergistic effect of Si-P-Cu-Cr elements, the weather resistance index I is more than or equal to 7.0, and the weather resistance index I has good atmospheric corrosion resistance. Thickness: 1.5-3.0 mm, tensile property: yield strength R_eL380MPa or more, the tensile strength Rm is 490MPa or more, and the elongation A is 28% or more. The outer side surface of the sample is not subjected to double cold bendingCracks appear, and the cold-bending forming performance is good.

Drawings

FIG. 1 is a typical metallographic structure of a steel sheet according to an example of the present invention, and shows ferrite having an average grain size of 10 μm and a volume fraction of 91.5%.

FIG. 2 is a hot rolled portion of a hot rolled steel strip produced by an example of the present invention, without cracks;

FIG. 3 shows the surface of a hot-rolled steel strip produced according to an example of the invention, without cracks.

Detailed Description

The technical solution of the present invention is further illustrated by the following specific examples.

Example 1 to example 6

The thin-specification Ni-free weathering steel produced based on the CSP process comprises the following components in percentage by mass: as shown in table 1, the balance not shown in table 1 is Fe and inevitable impurities. The weather resistance index I of each embodiment is more than or equal to 7.0, and the weather resistance index I has excellent atmospheric corrosion resistance.

Comparative example 1

Example 4, publication No. CN 105603320 a, was used as comparative example 1; the specific components are shown in table 1, and the balance not shown in table 1 is Fe and inevitable impurities.

Comparative example 2

Example 10, publication No. CN 111850396a, was used as comparative example 2; the balance not shown in table 1 is Fe and inevitable impurities.

As can be seen from Table 1, comparative example 1, which contains the noble alloy Ni, is high in manufacturing cost; the contents of Si, Mn and Cu of the comparative example 2 are all higher than those of the present invention, and the manufacturing cost is high.

TABLE 1 chemical composition of examples of the invention and comparative examples

Note: comparative example 2 also controlled N: 0.003%.

The production method of the thin-specification Ni-free weathering steel produced based on the CSP process in the embodiments comprises the following process flows: molten iron pretreatment deep desulfurization → converter top and bottom combined blowing → LF refining → thin slab continuous casting → CSP slab heating → CSP hot continuous rolling → laminar cooling → coiling.

Smelting molten steel according to the chemical components, controlling the superheat degree of the molten steel of a tundish in the continuous casting process to be 10-30 ℃, and controlling the main physical and chemical performance indexes of the covering slag as follows: alkalinity of 0.8-1.3, viscosity of 0.10-0.30 Pa.s, and melting point of 1022-1152 ℃. The thickness of the continuous casting slab is 60-90 mm, and the pulling speed of the continuous casting slab is controlled to be 3.5-4.5 m/min according to the width and the thickness of the casting slab. After cutting, the casting blank enters a roller hearth type heating furnace to be heated, and the charging temperature is more than or equal to 1000 ℃. Firstly, heating a plate blank for 20-35 min at the tapping temperature of 1130-1200 ℃. And (3) after the slab is taken out of the furnace, removing surface iron scales by high-pressure water descaling, and then rolling by adopting a 7-stand four-roller CVC continuous rolling unit. The reduction rates of F1, F2 and F3 are more than 50 percent, and the reduction rates of F6 and F7 are less than 10 percent; the running speed of the strip steel discharging F7 is controlled to be 7-12 m/s. And controlling the finishing temperature to be 840-900 ℃. And after finishing the finish rolling, carrying out laminar cooling at a cooling speed of 50-100 ℃/s and controlling the coiling temperature at 570-630 ℃. And naturally cooling to room temperature after coiling.

The main process parameters of the continuous casting process, the main process parameters of the rolling process and the mechanical properties of each example and comparative example are shown in tables 2, 3 and 4, respectively. Tensile properties test according to GB/T228.1-2010 "metallic materials tensile test part 1: the test method for the room temperature is carried out, and the cold bending performance test is carried out according to GB/T232-2010 metal material bending test method.

TABLE 2 main process parameters for continuous casting of inventive and comparative examples

TABLE 3 Main Process parameters of the Rolling sequence of the inventive and comparative examples

TABLE 4 mechanical Properties and surface qualities of inventive and comparative examples

The invention adopts the chemical components and the design of the controlled rolling and controlled cooling process, so that the microstructure of the steel plate is polygonal ferrite plus pearlite, the average grain size of the ferrite is 8-12 mu m, the volume fraction of the ferrite is 90-92%, and the typical metallographic structure is shown in figure 1.

A72 h periodic immersion corrosion test was performed according to TB/T2375, with the pattern dimensions: 40 mm. times.60 mm. times.2 mm, the test results are shown in Table 5 for the Q345B low alloy steel as the comparative sample, and the results of comparative example 2(CN 111850396A) are shown in Table 6. The atmospheric corrosion resistance of each example is improved by 1 time compared with the low alloy steel Q345B, and the alloy steel is at the same level as the comparative example 2, and has good atmospheric corrosion resistance. But the alloy of comparative example 2 costs significantly more than the present invention.

TABLE 5 atmospheric corrosion resistance of each of the examples and comparative examples

	Average corrosion weight loss rate, (g/(m)²·h))	Relative corrosion rate%
			Example 1	/	/
Example 2	/	/
			Example 3	2.27	52
Example 4	2.00	46
			Example 5	2.07	47
Example 6	/	/
			Q345B	4.37	100

TABLE 6 atmospheric corrosion resistance of comparative example 2 and comparative sample

In conclusion, the thin-specification Ni-free weather-resistant steel plate produced in the CSP sheet billet continuous casting and rolling process according to the technology solves the difficult problem of surface crack of continuous casting breakout and hot rolled coils, has yield strength of more than or equal to 380MP, tensile strength of more than or equal to 490MPa and elongation of more than or equal to 28 percent, has good atmospheric corrosion resistance and cold bending forming performance, and can be applied to manufacturing containers, photovoltaic supports, cable bridges and the like.

Claims

1. The thin-specification Ni-free weathering steel produced based on the CSP process is characterized by comprising the following components in percentage by mass:

c: 0.04-0.06%, Si: 0.30-0.55%, Mn: 0.30-0.80%, P: 0.020 to 0.150%, S: less than or equal to 0.005 percent, Cr: 0.30% -0.80%, Cu: 0.25-0.40%, Als: 0.015% -0.040%, Ti: 0.010-0.040%, the rest is Fe and inevitable impurity elements.

2. The thin gauge Ni-free weathering steel produced based on CSP process according to claim 1 characterized in that it has I ≥ 7.0.

3. The thin gauge Ni-free weathering steel produced based on CSP process according to claim 1, wherein the thin gauge Ni-free weathering steel produced based on CSP process has a thickness: 1.5-3.0 mm, tensile property: yield strength R_eL380MPa or more, the tensile strength Rm is 490MPa or more, and the elongation A is 28% or more.

4. A production method of thin gauge Ni-free weathering steel based on CSP process according to any of claims 1-3, characterized in that it comprises the following process flows: molten iron pretreatment deep desulfurization → converter top and bottom combined blowing → LF refining → thin slab continuous casting → CSP slab heating → CSP hot continuous rolling → laminar cooling → coiling.

5. The production method according to claim 4, characterized in that said thin slab continuous casting is in particular: controlling the superheat degree of the molten steel of the tundish at 10-30 ℃; the main physical and chemical performance indexes of the special protective slag are as follows: : alkalinity of 0.8-1.3, viscosity of 0.10-0.30 Pa.s, and melting point of 1022-1152 ℃.

6. The production method according to claim 4, characterized in that the CSP slab heating is in particular: the charging temperature is more than or equal to 1000 ℃, the heating time is 20-35 min, and the discharging temperature is 1130-1200 ℃.

7. The production method according to claim 4, characterized in that the CSP hot continuous rolling is in particular: and controlling the finishing temperature to be 840-900 ℃.

8. The production method according to claim 4, characterized in that the laminar cooling is in particular: the cooling rate is 50-100 ℃/s.

9. The production method according to claim 4, characterized in that the coiling is in particular: the coiling temperature is controlled to be 570-630 ℃.